There has been significant progress in the development of antibody-based therapies over the years. For example, investigators have identified not only a variety of cancer-specific markers but also a variety of antibodies that specifically bind to those markers. Antibodies can be used to deliver certain molecules, for example, a toxin or an immune stimulatory moiety, for example, a cytokine, to a cancer cell expressing the marker so as to selectively kill the cancer cell.
The 14.18 antibody is a mouse-derived monoclonal antibody directed against the cell surface glycosphingolipid GD2. GD2 is a disialoganglioside that is normally only expressed at a significant level on the outer surface membranes of neuronal cells, where its exposure to the immune system is limited by the blood brain barrier.
Many tumor cells, in contrast, have abnormal levels of glycosphingolipid cell surface expression. For example, GD2 is expressed on the surfaces of a wide range of tumor cells including neuroblastomas, medulloblastomas, astrocytomas, melanomas, small-cell lung cancer, osteosarcomas and other soft tissue sarcomas. Thus, GD2 is a convenient tumor-specific marker for targeting immune-stimulatory protein domains to tumor cells for the purpose of raising an effective immune response against the tumor cells to destroy them. While the 14.18 mouse antibody (m14.18 antibody) may assist the targeting of these protein domains to tumor cells, its mouse-derived amino acid sequences can impair the desired therapeutic effect.
When administered to a patient, antibodies can have an associated immunogenicity in the host mammal. This is more likely to occur when the antibodies are not autologous. Consequently, the effectiveness of antibody-based therapies often is limited by an immunogenic response directed against the therapeutic antibody. This immunogenic response typically is increased when the antibody is derived in whole or in part from a mammal different than the host mammal, e.g., when the antibody is derived from a mouse and the recipient is a human.
For clinical use in humans, it may be helpful to modify mouse-derived antibodies to more closely resemble human antibodies, so as to reduce or minimize the immunogenicity of the mouse-derived antibody. The immunogenicity of the mouse-derived antibody can be reduced by the creation of a chimeric antibody in which the constant regions of a human antibody are fused to mouse variable domains. However, the remaining mouse variable domains are generally still immunogenic in humans, and can thus impair the efficacy of an antibody-based therapy.
Some approaches to reducing immunogenicity, such as “veneering” and “humanization” involve the introduction of many amino acid substitutions and may disrupt the binding of an antibody to an antigen. The m14.18 antibody binds to GD2 with moderate affinity. Therefore, mutations that significantly lower the affinity of m14.18 for GD2 are expected to make it less effective for therapeutic purposes in humans. Accordingly, there is a need in the art for therapeutic antibodies that can effectively target GD2 and have reduced immunogenicity when administered to a human.